The sheet materials to which this invention is directed are usually referred to in the art as "electrical" silicon steels or, more properly, silicon-irons and are ordinarily composed principally of iron alloyed with about 2.2 to 4.5 per cent silicon and relatively minor amounts of various impurities and very small amounts of carbon. These products are of the "cube-on-edge" type, more than about 70 per cent of their crystal structure being oriented in the (110)[001]texture, as described in Miller Indices terms.
Such grain-oriented silicon-iron sheet products are currently made commercially by the sequence of hot rolling, heat treating, cold rolling, heat treating, again cold rolling and then final heat treating. Ingots are conventionally hot-worked into a strip or sheet-like configuration less than 0.150 inch in thickness, referred to as "hot rolled band." The hot rolled band is then cold rolled with appropriate intermediate annealing treatment to the finished sheet or strip thickness involving at least a 50 per cent reduction in thickness, and given a final or texture-producing annealing treatment.
In the preferred practice, the hot rolled band, having a thickness of 80 to 100 mils, after heat treating is cold rolled to about 30 mils. heat treated for an intermediate anneal, again cold rolled to final thickness, which may be about 10 to 14 mils commercially, and then finally annealed for decarburization and secondary recrystallization. Thus, the cold-rolling operation, in present practice, is done in two stages, with the intermediate anneal at about 900.degree.-950.degree.C. This intermediate heat treatment makes possible the development of strong cube-on-edge secondary recrystallization textures during the final anneal.